The present invention relates to the design and construction of a closure assembly that includes a receiving flange, a seal, and a closing plug that is constructed and arranged to be received by the flange. The receiving flange is secured to a container, such as in the drum end of a large industrial container. More specifically, the present invention relates to a unique design and construction for the closing plug of the closure assembly that includes in one embodiment a torque-limiting feature. In a related embodiment of the present invention, the closing plug is constructed and arranged to capture the seal.
Large, industrial, metal containers are typically configured with a filling/dispensing opening and a smaller vent opening. These openings must be securely and tightly closed and sealed whenever product is shipped. These are normally over-the-road shipments and several Department of Transportation (D.O.T.) standards or regulations apply. While there may be any number of additional industry standards depending on the container specifics and the product being shipped, it is important for the container openings to be securely closed and the realities of the container construction and the applicable D.O.T. standards dictate a fairly limited range of design options for fabricating and closing the two openings. One of these container construction realities is the limited thickness of the metal comprising the drum end where the two openings are typically and preferably located.
One fabrication technique that has proven to be successful is to pierce an opening in the metal drum end or “head” and form the surrounding metal into a raised receiving boss. An internally-threaded metal flange with a serrated peripheral edge is then assembled into the receiving boss. A metal forming operation follows and this operation shapes the drum end metal around the serrations as well as under and over the flange in order to securely and tightly anchor the flange into the receiving boss. The forming operation is performed in a manner that results in the drum end metal overlaying the upper surface of the flange immediately adjacent the threaded opening of the flange. The flange thickness in the area of the threads is greater than the material thickness of the drum end, thereby enabling a sufficient number of threads to be formed in the flange for receipt of the closing plug. The drum end alone is too thin to yield a sufficient number of threads for adequate threaded capture of the closing plug based upon the applicable D.O.T. standards that have to be met.
Since the transported, stored, and dispensed contents of containers (i.e., drums) of the type described are liquid, it is important to include an annular gasket or seal that is compressed between the drum end metal that overlays the flange and the plug surface to help seal the interface between the flange and the closing plug. One of the concerns expressed for this type of closure is the possibility that the closing plug is not properly tightened into the receiving flange. This could be either not tightened enough to adequately compress the seal or tightened too much such that the seal looses its resiliency.
Typically, the determination of proper plug tightening relies on a torque wrench and proper tightening by the filler of the drum. Visually, there is no way to tell if the closing plugs have been properly installed and thus a drum shipment could be loaded where one or more of the plugs do not meet the D.O.T. requirements. If the truck is stopped and the load inspected by a D.O.T. officer, it could fail the D.O.T. inspection. The inspection procedure includes applying a torque wrench to one or more of the closing plugs of the shipment in order to test whether those plugs are properly tightened and meet the torque level set by the D.O.T. If any one closing plug is not properly tightened, the container fails and the entire shipment can be rejected and must then be returned in order to have all of the closing plugs checked and tightened. Since each drum is not checked by the D.O.T. officer and since many or most of the drums could in fact meet the D.O.T. requirements, the penalty of finding any one closing plug that is not properly tightened is relatively harsh.
In order to address this concern, a first embodiment of the present invention was conceived and includes a new design for the closing plug such that visual confirmation can be made as to whether or not the closing plug is properly tightened into the receiving flange such that it will pass the D.O.T. inspection. An additional benefit derived from the present invention is the ability to set the torque on the closing plug within the desired range such that the cooperating annular seal is properly compressed. Importantly, all of this occurs without the need to utilize a torque wrench at the time of filling or at the time of shipment.
These invention benefits are achieved by redesigning the closing plug to include axially-protruding portions that abut up against that portion of the drum end that overlays the upper surface of the receiving flange. By properly sizing the axial length of these protruding portions based on the thread pitch of the plug and flange, any taper of the plug threads, and the size and composition of the annular gasket, the desired tightening torque occurs as the advancing surface of each protruding portion first contacts the drum end portion overlaying the receiving flange, according to the first embodiment of the present invention. Preferably, the desired tightening torque is reached and the protruding portions then abut up against the drum end portion within one further revolution of the closing plug. Ideally, abutment occurs within one-half of a revolution of the closing plug.
The plug construction, according to the first embodiment of the present invention, provides a unique torque limiting structure that also provides a visual indication of whether or not the proper torque has been set on the closing plug. If the protruding portions are in contact with the drum end portion, then it is known, based on the calculations that can be performed, that the correct tightening torque for the closing plug is “automatically” set. Once it is understood that protruding portion contact equates to the proper torque setting, any D.O.T. inspection can be done visually. Importantly, the filler and/or shipper can also perform a visual inspection at any time after the plug is threaded into the receiving flange. This enables the filler and/or shipper to ensure that whatever containers are loaded for shipment will pass any D.O.T. inspection.
Another benefit of the present invention relates to the axial compression of the annular gasket. A square-cut annular gasket may be used or an O-ring gasket can be used. With a square-cut circular gasket that has an inside diameter size slightly smaller than the outside diameter of the plug at the assembly location, the gasket can actually be preassembled to the plug. As the plug is tightened, the gasket is compressed. Since there is nothing surrounding or enclosing the gasket in the prior art arrangement, it is possible for the gasket to move radially outwardly as plug compression occurs. With a fixed volume of material, this radial movement reduces the axial thickness of the gasket, potentially requiring additional threaded advancement of the plug into the flange in order to achieve the requisite sealing.
A first embodiment of the present invention focuses on the abutment of the protruding portions against the drum end portion overlaying the flange. A second embodiment of the present invention focuses on the use of the protruding portions as a structure that encloses the gasket, thereby controlling any radial shift and/or radial expansion. With the present invention, the protruding portions are positioned radially outwardly of the gasket and, as a result, they actually enclose the gasket. Depending on the size of the gasket, its material and compressibility, and depending upon its positioning or alignment relative to the plug, if there would be the risk of substantial outward radial movement of the gasket during compression, the protruding portions are effective to capture the gasket and limit any such outward radial movement and thereby help to maintain an axial thickness for proper sealing. Accordingly, the structural improvement made to the closing plug in the form of the protruding portions constitutes a novel and unobvious advance in the art.